With the spread of laptop computers, mobile phones, digital cameras, and the like, the demand for secondary batteries for driving these small-sized electronic devices has been expanding. Further, for these electronic devices, lithium batteries have been increasingly used for their capability to achieve high capacity.
In addition to the use for these small-sized electronic devices, the application of lithium batteries for vehicles (EV, HV, PHV), household power supplies (HEMS), and the like, where a large amount of electric power is required, has also been considered.
In a lithium battery (e.g., lithium ion secondary battery), generally, a positive electrode plate and a negative electrode plate are laminated with a separator therebetween to form an electrode assembly, and the electrode assembly is housed in a case together with a nonaqueous electrolyte (electrolytic solution).
In a conventional lithium battery, an electrolytic solution containing a flammable organic solvent is used. Therefore, it is necessary to install a safety device to suppress the exothermic reaction in case of short-circuiting or improve the structure or materials to prevent a short circuit.
In order to deal with this problem, it has been considered replacing the electrolytic solution with a solid electrolyte layer to make an all-solid-state battery. Because a flammable organic solvent is not used in the battery, such an all-solid-state lithium battery allows for the simplification of a safety device and is excellent in terms of production cost and productivity.
A solid electrolyte layer for an all-solid-state lithium battery can be formed from the solid electrolyte material described in PTL 1 or 2.
PTL 1 describes a solid electrolyte represented by LixMOyNz (wherein M is at least one element selected from the group consisting of Si, B, Ge, Al, C, Ga, and S, and x, y, and z satisfy x=0.6 to 5.0, y=1.050 to 3.985, and z=0.01 to 0.50, respectively).
PTL 2 describes a technique in which GeS2 or Sb2S3, which is stable in air, is added to a Li2S—P2S5-based sulfide solid electrolyte material containing unreacted Li2S, thereby eliminating unreacted Li2S.
However, the solid electrolyte material described in PTL 1 has a problem in that in an N-rich system, a decrease in ion conductivity cannot be prevented.
The solid electrolyte material described in PTL 2 can exert effectiveness in reducing the amount of hydrogen sulfide generated, but the generation of hydrogen sulfide cannot yet be completely prevented. In addition, hydrogen sulfide may be generated not only from the reaction with moisture but also in the case of battery abnormalities.
PTL 1: JP-2005-38844 A (corresponding to US 2007/0042272 A1)
PTL 2: JP-2011-129407 A